1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. In particular, the present invention relates to, for example, a semiconductor device, a display device, a light-emitting device, a power storage device, a memory device, a driving method thereof, or a manufacturing method thereof. Specifically, one embodiment of the present invention relates to a semiconductor device, particularly a semiconductor device including an oxide semiconductor.
2. Description of the Related Art
In a transistor in which an oxide semiconductor (OS) is used for a semiconductor layer where a channel is formed (such a transistor is also referred to as an OS transistor), the threshold voltage of the transistor can be controlled by supplying appropriate voltage to a back gate (see, for example, Patent Document 1).
A back gate is an electrode which is a counterpart to a front gate. The back gate and the front gate are provided with a semiconductor layer including a channel formation region provided therebetween. For example, in a bottom-gate transistor, a gate under a channel formation region is a front gate and a gate over the channel formation region is a back gate. Note that a front gate and a back gate are called a first gate and a second gate, respectively, in some cases.
In an OS transistor with a so-called dual gate structure in which a back gate is connected to a front gate, the current value in a conduction state can be efficiently increased even when the OS transistor has smaller size (see, for example, Patent Document 2). For example, a dual-gate transistor is used in a gate driver of a display device, whereby the display device can have a narrow frame.